Clathrate compound formation



March 1954 c, J. BUSSO ET AL 2,673,195

CLATHRATE COMPOUND FORMATION Filed June 25, 1948 "L Non-Si'mi hf Chain Hqdrocaibons agga L ,7 B.P ao-s2s:=

Number 6 Fraci'bna+or A QaFfinafe Corfial'nln Nonsh'aiqhfi' Chain Ciasolme Hqdr-ocarbons 5.9 eoMoF 6P. 315-440? A. Urea:

5 SH-ai hi" chain Hqoirocarbons anal Non -5i'miqh+ Chain Hgdrocarbons 5 B p 215 40 F clai'hrafe l Compounds 0P Urea and 51-miqhf Chain Hqdroanrbons lrwenrors Ernesr Lwafl'ars Charles J. Busso Patented Mar. 23, 1954 UNITED STATES PATENT OFFICE CLATHRATE COBIPOUND FORMATION poration of Delaware Application J une 25, 1948, Serial No. 35,106

This invention relates to a process for the formation of clathrate compounds. More particularly, it is concerned with an improved process for the fractionation of mixtures of organic materials by the formation of clathrate compounds with certain fractions thereof.

The fractionation of petroleum hydrocarbons is usually carried out by closely controlled distillation. Further processing for the removal of specific fractions, such as aromatics, is sometimes employed for the purpose of obtaining special products. Other mixtures of organic compounds require the use of fractional techniques in order to obtain products having a particular utility.

It is known that gasoline distillates comprise a mixture of hydrocarbons having various typical configurations. Essentially, these include straight-chain, branched-chain, and cyclic hydrocarbons, both saturated and unsaturated. Further, it is known that the octane rating of a gasoline varies inversely with the concentration of the straight-chain hydrocarbons in such gasoline. It follows that the removal of straightchain hydrocarbons from a gasoline will result in a product having an improved octane number.

Certain compounds have been found to have the property of forming compounds which may be termed as clathrate compounds. By the latter term is meant the general type of compound in which the one component imprisons another without necessarily having any strong attractive interaction with it. Outstanding examples of clathrate-forming materials are those having the general configuration:

wherein X is oxygen, sulfur, selenium r tellurium. Salts of these compounds, such as acetates and hydrochlorides, also form clathrate compounds. The most generally recognized reaction of this type comprises the formation of clathrate compounds between urea and straight-chain hydrocarbons. It has been found that such formation may be conducted in the presence of other types of hydrocarbons without the latter being affected. These clathrate compounds are crystalline materials which readily separate from liquid media upon their formation; hence, this clathrate-compound formation may be utilized for the separation of straight-chain hydrocarbons from gasoline distillates for the purpose of obtaining a rafiinate having an improved octane rating.

9 Claims. (Cl. 26096.5)

The portion of any mixture which does not react with the clathrate-forming agent is to be considered as a "ramnate for the purpose of this discussion.

Gasoline distillates vary widely in their composition, depending primarily upon the crude source from which they are obtained. Mid- Continent gasoline stocks, for example, normally contain straight-chain hydrocarbons over the whole boiling range of the distillate. In this case, it usually becomes essential to treat the entire distillate with urea in order to obtain maximum octane improvement. Other distillates, such as those obtained from San Joaquin Valley crude, differ in that they normallycontain a relatively insignificant amount of lower-boiling straight-chain hydrocarbons, even though they have a substantial proportion of higher-boiling straight-chain hydrocarbons.

Investigation of the phenomenon of clathrate formation has disclosed the fact than an equilibrium is reached in the reaction mixture with regard to the proportion of straight-chain hydrocarbons which may be extracted from a mixture under a given set of conditions. For example, when operating at room temperature, it has been found that after treatment with urea a reaction mixture will always contain a certain proportion of unreacted straight-chain hydrocarbons even though an excess of urea has been present. Various influences, to be discussed hereinafter, affect this equilibrium.

It is an object of this invention to improve the process of clathrate-compound formation. It is another object of this invention to apply this improved process to the extraction of petroleum distillates. It is specific of this invention to improve the octane rating of gasolines having substantially-no lower-boiling straight-chain hydrocarbons by the use of an improved process of clathrate compound formation.

Now, in accordance with this invention, it has been found that the efficiency of clathrate compound formation may be substantially improved by concentrating the reactive materials prior to contacting with the clathrate-forming agent. This invention is especially applicable to the treatment of hydrocarbon mixtures with urea, and especially to gasoline distillates containing substantially no lower boiling straight-chain hydrocarbons by having an appreciable amount of higher-boiling straight-chain hydrocarbons. As more particularly pointed out hereinafter, the straight-chain hydrocarbons may be paraffinic or Qlefinic, while the non-straight-chain may be branched paraffins, branched olefins, aromatics, cycloparafilns, naphthenes, etc.

A specific embodiment, as illustrated by the example appearing hereinafter, comprises the fractionation of such a gasoline distillate, preferably by means of careful distillation, into two fractions, A and 'B. The fraction Acontains all of the lower-boiling hydrocarbons present in the original distillate, preferably boiling below 300 F. and having less than 9 carbon atoms. These will be non-straight-chain hydrocarbons, for the most part, together with any minor proportion of straight-chain hydrocarbons boiling in this lowerboiling range. The fraction B contains hydro.- carbons boiling above the range of those present in fraction A and will comprise a mixture of straight-chain hydrocarbons and non-straightchain hydrocarbons, preferably boiling above 300 F. and having more than 8 carbon atoms. The application of the present invention, then, comprisesitreatingonlyfraction B :with. a clathrate' formingagent, such as urea, whereby the straightchainhydrocarbons crystallizeout in theform-of clathrate compounds with urea, leavingas-a raf-' finate the-higher-boiling non-straight-chain hydrocarbons. Therafiinate thencomprises a heavy gasoline havingsubstantially improved octane number: This raflinate. subsequently may be" blended, if desired',vwith--at:least part of fraction A-or with any'other desired gasoline distillatein order; to obtain; a r gasoline substantially free of straight-chain hydrocarbons and having an improved octanerating.

Therapplication of theproces described above results inseveraladvantagesh The product obtained by the treatment of only; the -higher-bcil-- ing; fraction is. at least: asigoodz as,- andusually betterthan, that which. results from the treatment of the Whole mixture.:. Iffthe finalproduct obtained by thenpresentinvention istbetter'than thatv resulting from thextreatment of th Whole mixture, this isdue to the equilibrium phenomenon discussed hereinbefore: However, even when products of equal quality; are obtained, the important advantages of' the present :process include reduction in operationallosses and substantial; reduction in apparatus-- requirements;

The process applies b'oth'vto hydrocarbon mixtures 'having'no straight-chain; lowereboiling. hydrocarbons and :to .mixtureshavingronly a minor amount: thereof: Th claims; and specification are considered to relate to both of:th'esesitua'- tions.-;

The use-of urea in clathrate compound-formation' makes possible the formation: of? a. widevariety of products, dependent upon the" condi-- tions of :the treatment, which, are employed, The

process is preferably "conducted 'attemperatures ranging: from about to =about 125? although, higher or'lower temperatures-may be found suitable in certain: instances: Preferably; the clathrate? formation is carried out within" the Contact is usually Obtained. by intimate mixing'of -ureawiththe hydrocarbon mixture; Pref+ erably, this is conducted in a continuous manner' sinc -it" has been" found that continuouslyformed clathrate compounds possess crystal structures whichfavor their separationfrom the raffinate.

Thev clathrate-forming agent, such as .urea, is preferably, dissolved in. a suitable. solvent, although it. may be usedinspecial instances in crystalline form.. Solvents. which have. been found to have particularv advantages. include:

water and aqueous alcohol. In order to obtain maximum clathrate compound formation, the solution should be maintained at all times as nearly saturated as possible with respect to the treating temperatures. In order to maintain saturation, additional urea may be added during the process. Alternatively, a large excess of urea solution may be employed with respect to the quantity of straight-chain hydrocarbons to be extracted. When stocks contain from eight to twenty percentstraight-chain hydrocarbons and when the treating temperature is 5-25 C., the ratio of saturation aqueous urea solution to the hydrocarbon'mixture is preferably between about 2:11an'd 10:1.

Certain polar solvents for the hydrocarbon mixturehavezbeen found to promote the maximum rate of complex formation and appear to aidin obtaining optimum crystalline structure, as well as to favor maximum clathrate compound formation.- Solvents of this "nature include-especially-the-alcoholshaving four or five"v carbon=- atoms-and the'ketones bearingalkyl groups hav ing-from one to five carbonatoms each. Species:

of these solvents include secondary butyl alcohol, tertiary butyl alcohol, secondary; amyl alcohol, methyl ethyl ketone and. methyl isobutyl ketone.

Inorder to obtain the optimum effect of the: use;. of such-diluents, they shouldbe used in a ratio with the hydrocarbon mixtureoffrom 3: 1 to 1:4;

The inclusion of certain surface-active agents" in' the reaction mixturehas been-found to-favor' separation of clathrate compounds from: the" Unless special precautions are taken;

rafiinate. the surface of the clathrate crystalsroccludes substantial amounts of the ralfinate materials; It is-especially desirable, therefore, tolemploy a system" wherein the clathrate crystals 1 separate cleanly from the raflinate and associate'entirely with the'urea solution; Furthermore, due to: the apparent adherence of. the-raflinate to thez'cla thrate surfaces, the normal mixture" is largely" This results in vis:-'-

thixotropic in character. cositydifiiculties' during the separation of. the clathrate compounds from" the raffinate: inclusion ofcertain types of surface-active agents in the reaction mixture has been'lfound to favorably modifythe thixotropic character thereof and to. aid in causing the rafiinate:torseparatefrom the 'clathratecrystals, the latter. tending'to as-- sociate with theaqueous phase.

Suitable typesof surface-active agents include the alkali metal salts of organicsulfonic acids- Other suitable types ofsurface-active agents. are high molecular weight secondary alcohols;

such as 7-ethyl-2-methyl-undecanol+4.

The surfaceactive agentsmay be employed-in amounts-varying from about 0.1 to aboutt5z0.

per cent, based on theweight of the hydrocarbon mixture. Their use causesthe reaction system to have=a reduced viscosity andto settle more rapidly into :an upper" and lower layer, the .upper.

layer comprising the raflinate hydrocarbons" and the lower layer comprising the remaining aqueous urea solution andthe clathrate compounds;

The present" process also. may. be" applied.- to: mixtures of hydrocarbons other: than: those .containing the special type of gasoline distillatemde scribed hereinbefore. These may be hydrocarbon The? ae'ra, 19c

mixtures obtainedby the polymerization of natural gas or synthetic mixtures containing hydrocarbons having from four to sixteen carbon atoms. Straight-chain hydrocarbons forming clathrate compounds with urea include especially those having at least seven carbon atoms, such as oc-- tane, decane and dodecane. The principle upon which this invention is based applies as well to the fractionation of mixtures of polar compounds, such as alcohols, aldehydes, ketones, acids and esters.

The process is particularly described in the accompanying diagram, wherein a gasoline distillate having a boiling range of 90-410 F. was employed. Ten parts by volume of saturated aqueous urea solution were contacted with a mixture of two parts of the gasoline and one part of methyl ethyl ketone at a treating temperature within the range of -70" F. The gasoline stock was one obtained from a San Joaquin Valley petroleum crude and contained substantially no straight-chain hydrocarbons boiling below about 325 F.

The stock I was fractionated into two fractions by distillation. The fratcion 2 boiled from 90 to 325 F. and contained only non-straightchain hydrocarbons in this boiling range. The higher boiling fraction 3 had a boiling range of 325-410 F. and contained both straight-chain hydrocarbons and non-straight-chain hydrocarbons in this boiling range. The fraction 3 was treated with urea solution 4 as described above. The crystalline clathrate compounds 5 which formed between urea and the straight-chain hydrocarbons present in fraction 3 were separated from the unaffected raflinate by filtration. The raffinate 6, comprising non-straight-chain hydrocarbons having a boiling range of 325-410 R, was combined with fraction 2 to give a blend '1 having substantially improved octane rating.

The original gasoline distillation had an octane number of 49. The blend '1, obtained as described above, had an octane rating of 56. For comparison, the original gasoline distillate having a boiling range of 90-4=l0 F. was treated with urea solution without being subjected initially to fractional distillation. The rafiinate from this reaction also had an octane rating of 56.

The fractions 2 and 3, described above, were substantially equal in size; hence, the full improvement in octane possible has been obtained by the process of the present invention, although only fifty per cent of the original distillate was treated. The economical and technical advantages of such a process are immediately evident.

We claim as our invention:

1. In a process for the fractionation of hydrocarbon mixtures comprising straight-chain. hydrocarbons and non-straight-chain hydrocarbons wherein said mixtures are contacted with an aqueous urea solution whereby crystalline molecular complexes are formed between urea and straight-chain hydrocarbons and subsequently are separated from the non-crystalline components, the improvement which comprises conducting said contacting and separation in the presence of from about (2.1% to about 5% by weight based on the hydrocarbon mixture of a surface-active agent of the group consisting of sodium salts of allryl aryl sulfonic acids, sodium salts of alkylated sulfo-succinic acid and high molecular weight secondary alcohols.

2. In a process for the fractionation of hydrocarbon mixtures comprising straight-chain hydrocarbons and 'non-straight-chain hydrocarbons wherein said mixtures are contacted. with an aqueous urea solution whereby crystalline quently are separated from the non-crystalline 7 components, the improvement which comprises conducting said contacting and separation in the presence of from about 0.1% to about 5% by weight based on the hydrocarbon mixture of a sodium salt of alkyl aryl sulfonic acids.

3. In a process for the fractionation of hydrocarbon mixtures comprising straight-chain hydrocarbons and non-straight-chain hydrocarbons wherein said mixtures are contacted with an aqueous urea solution whereby crystalline molecular complexes are formed between urea and straight-chain hydrocarbons and subsequently are separated from the non-crystalline components, the improvement which comprises conducting said contacting and separation in the presence of from about 0.1% to about 5% by weight based on the hydrocarbon mixture of an sodium salt of alkylated sulfosuccinic acid.

4. In a process for the fractionation of hydrocarbon mixtures comprising straight-chain hydrocarbons and non-straight-chain hydrocarbons wherein said mixtures are contacted with an aqueous urea solution whereby crystalline molecular complexes are formed between urea and straight-chain hydrocarbons and subsequently are separated from the non-crystalline components, the improvement which comprises conducting said contacting and separation in the presence of from about 0.1% to about 5% by weight based on the hydrocarbon mixture of a high molecular weight secondary alcohol.

5. A process according to claim 1 wherein the hydrocarbon mixture is a gasoline distillate.

6. In a process for the fractionation of hydrocarbon mixtures comprising straight-chain hydrocarbons and non-straight-chain hydrocarbons wherein said mixtures are contacted with an aqueous urea solution whereby crystalline molecular complexes are formed between urea and straight-chain hydrocarbons and subsequently are separated from the non-crystalline components, the improvement which comprises conducting said contacting and separation in the presence of from about 0.1% to about 5% by weight based on the hydrocarbon mixture of 7- ethyl-2-methyl undecanoli.

7. In a process for the fractionation of hydrocarbon mixtures comprising straight-chain hydrocarbons and non-straight-chain hydrocarbons wherein said mixtures are contacted with an aqueous urea solution whereby crystalline molecular complexes are formed between urea and straight-chain hydrocarbons and subsequently are separated from the non-crystalline components, the improvement which comprises conducting said contacting and. separation in the presence of from about 0.1% to about 5% by weight based on the hydrocarbon mixture of the sodium salt of diamyl sulfosuccinic acid.

8. In a process for the fractionation of hydrocarbon mixtures comprising straight-chain hydrocarbons and non-straight-chain hydrocarbons wherein said mixtures are contacted with an aqueous urea solution whereby crystalline molecular complexes are formed between urea and straight-chain hydrocarbons and subsequently are separated from the non-crystalline components, the improvement which comprises conducting said contacting and separation in the pres- 811681 tofifmm about 0.1% to about '5 I by: :weight based: on i the :-hydrocarbon r 1 mixture of rsodium' dodecylrzmethylphenylsulfonate.

9; In the. process for the formation; precipita tionand separationof crystalline molecular com plexes by contacting a higher straightchainalkane having at least seven carbon atoms with urea in-aqueous solution, the improvement which consists-in adding solely a small amount of a surface active agent of the group consisting of sodium salts of alkylaryl sulfonic acids; sodium salts of alkylated sulfosuccinic acid and high molecular weight secondary alcohols to said aqueous solution.

CHARLES J. BUSSO.

ERNEST L. WALTERS:

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1,827,537" Morrell'i'; Oct, .13," 1931 2,025,255 Taylor et a1.. Dec. 24, 1935 T 2,115,960 I Lindeke May 3,1938 2,249,461 Diwoky July 15,1941" 2,383,768 Buis .etal Aug...28, 194511 2,499,236 Van Gilder et al'. Feb; 28, 1950 2,518,677 Garner Aug. 15, 1950 OTHER: REFEREN(JES Technical Oi1"Mission;Ree1143; 6 pages trans- 5 lation of German patent application No. B%

190,197 '(B'engen), deposited in theLib'rary' of" Congress, May 22, 1946. 

1. IN A PROCESS FOR THE FRACTIONATION OF HYDROCARBON MIXTURES COMPRISING STRAIGHT-CHAIN HYDROCARBONS AND NON-STRAIGHT-CHAIN HYDROCARBONS WHEREIN SAID MIXTURES ARE CONTACTED WITH AN AQUEOUS UREA SOLUTION WHEREBY CRYSTALLINE MOLECULAR COMPLEXES ARE FORMED BETWEEN UREA AND STRAIGHT-CHAIN HYDROCARBONS AND SUBSEQUENTLY ARE SEPARATED FROM THE NON-CRYSTALLINE COMPONENTS, THE IMPROVEMENT WHICH COMPRISES CONDUCTING SAID CONTACTING AND SEPARATION IN THE PRESENCE OF FROM ABOUT 0.1% TO ABOUT 5% BY WEIGHT BASED ON THE HYDROCARBON MIXTURE OF A SURFACE-ACTIVE AGENT OF THE GROUP CONSISTING OF SODIUM SALTS OF ALKYL ARYL SULFONIC ACIDS, SODIUM SALTS OF ALKYLATED SULFO-SUCCINIC ACID AND HIGH MOLECULAR WEIGHT SECONDARY ALCOHOLS. 